The invention relates to a conveying apparatus for the conveying of objects from a first station to a working station, comprising a first controllable conveyor with a first conveying path, a second controllable conveyor with a second conveying path, wherein the first conveying path and the second conveying path partly align and an object conveyed by the first conveyor can be taken over by the second conveyor at a take over position within the aligning zone of the conveying paths, and a control unit connected to the controllable drives of the conveyors. The invention further relates to a welding apparatus including such a conveying apparatus and still further relates to a welding method.
Such apparatus are for example used for can body making. The rounded but not yet welded can bodies are output from a rounding apparatus and then conveyed by the first conveyor in direction of the can body welding station. The objects or the not yet welded can bodies, respectively, are delivered with a delivery speed for the taking over by the second conveyer to the take over zone and handed over therein to the second conveyor. The second conveyor transports the can bodies into the welding station. Known conveyors for this work are provided with a crank drive or with a multi linkage system which acceleration and speed is dependent of the feed rate of the conveyed bodies and which conveying stroke length is essentially constant. The second conveying apparatus hands the can bodies over to the welding station with a speed that essentially equals the welding speed of the welding station. The transport means of the welding station transport the bodies with constant welding speed through the welding station and at the same time the axially aligned edges of the bodies are welded. During welding a very small distance between bodies following each other is necessary for high welding quality and the welding speed is usually less than the delivery speed of the second conveyor and at the most equals the delivery speed of the second conveyor.
The handing over of a body from the first conveyor to the second conveyor is usually effected by a conveying dog of the second conveyor that contacts the body from behind and accelerates the body, pushing it along the taking over path and, after the short acceleration, decelerating the body which is then taken over by the transport of the welding station while the conveying or taking over dog, respectively, returns to its starting point for taking over of the next body.
With a prior art conveying apparatus and welding apparatus, respectively, considerable changeover work is necessary when the size of the objects changes (which is the can body height in case of can bodies that are conveyed while lying horizontal). To this end the position of the first conveyor has to be adapted each time body height changes to the new body height which is very time consuming.